Process and devices for the electrolytic formation of a deposit on a chosen group of electrodes

ABSTRACT

A method and device for the electrolytic formation of a deposit on a group of electrodes of an electrolysis support. The support has a plurality of electrodes. Electric charges are selectively deposited on chosen electrodes. The support is placed in the presence of an electrolyte to produce the deposit on the chosen electrodes by electrolysis. The electric charges deposited on the electrodes provide an electrolysis current for each chosen electrode. The formed device may be used as a biological sensor.

This is a national stage application of PCT/FR97/10735, filed Oct, 1,1997.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a process and devices for the electrolyticformation of a deposit on a chosen group of electrodes of a substrate.

The invention finds application, in particular, in the manufacture ofsensors or other miniaturized sensing elements in which chips having ahigh number of electrodes must be made. For their adaptation to theirspecific function in the sensor or sensing element, these electrodesmust be selectively coated with appropriate materials.

As an example, the invention applies to the production of miniaturizeddevices such as <<biochips>> which are chips comprising an electriccircuit part fabricated on a substrate, and a biological part fabricatedon the surface of the chip. In this example, chemical compounds that arecompatible with the biological products must be selectively deposited onthe electrodes. In this respect, reference may be made to document (3)cited at the end of this disclosure.

By electrolytic formation of a deposit is meant both conventionaldepositing of a metal such as copper or nickel for example, and thedepositing of complex compounds obtained in particular from organicsubstances.

DISCUSSION OF THE BACKGROUND

To form a deposit on electrodes, recourse is currently made to knownmicroelectronics processes, such as lithography processes.

With these processes it is possible to treat a great number of chipssimultaneously on one same semiconductor section in order to selectivelydeposit a chemical compound on determined electrodes of each chip.

As is described by document (1) whose references are given at the end ofthis disclosure, said depositing process comprises the followingsuccessive stages:

depositing on the semiconductor section a continuous electric conductionbase in contact with the electrodes on which a deposit is to be made,

formation of a thin resin layer on the continuous base,

making openings in the resin above the chosen electrodes

electrochemical formation of the deposit material in these openingsusing the continuous base as an electrode, an independentcounter-electrode being placed in an electrochemical bath with thesemiconductor section,

removal of the resin and the continuous base around the depositedmaterial.

This is a conventional process. It can be used to deposit locally on onesection of the substrate, for example on determined electrodes, a metalor any other chemical compound.

However, for some applications, it is necessary to coat differentelectrodes of one same chip with different materials, these materialsbeing dedicated to the specific function of each electrode.

With the above-mentioned electrochemical process, in order to depositdifferent materials on different sites or electrodes of a semiconductorsection, it is necessary to form as many layers of resin as there aredifferent materials to be deposited. To deposit each material it isnecessary to expose the areas in which the material is to be depositedand to protect the areas where no deposit is to be made.

The succession of a great number of resin depositing stages andlithography operations to make the required number of openings in eachresin layer, corresponding to the electrodes which are to be coated witha given material, means that this is a complex process.

According to another technique which can be used to avoid thelithography stages and resin depositing, an electrolysis support is usedhaving individually addressable electrodes.

Depending upon the planned number of electrodes on the electrolysissupport, a direct addressing system or a multiplex addressing system maybe used in the support. In this respect, reference may be made todocument (2) cited at the end of this disclosure.

In the case of multiplex addressing, integrated switches are associatedwith the electrodes. Therefore, to make a selective electrolyticdeposit, it is merely required to selectively address a given group ofelectrodes by operating the closure of the appropriate switches and thusapplying to them the electrolysis current.

This technique is less complex than the first technique mentioned buthas the disadvantage of being costly.

In this case, an often complex and costly addressing system needs to beincluded in each electrolysis support. Also, this addressing system isof single use for each support and becomes unnecessary when thedifferent electrolytic deposits are completed.

It may be added that, according to the abovementioned techniques, thesupport comprising the electrodes must be immersed in an electrolyticbath while applying a set of polarizing or addressing voltages adaptedto the addressing system of the electrodes. This may raise problemsrelating to the insulation or protection of the support's contactconnections receiving the polarizing or addressing voltages.

SUMMARY OF THE INVENTION

The purpose of this invention is to remedy the difficulties of theabove-mentioned techniques.

One purpose of the invention is, in particular, to describe a processwhich does not require the formation of resin masks on the electrodesthat are not selected for depositing.

Another purpose of the invention is to allow the use of an electrolysissupport which does not necessarily have a complex, costly addressingsystem.

A further purpose of the invention is to avoid addressing the electrodeswhile the support is immersed in an electrolytic bath.

A further purpose of the invention is also to make available anelectrolysis support and a polarizing head adapted to the implementationof the process.

To reach the above-mentioned objectives, the invention sets out moreprecisely to describe a process for the electrolytic formation of adeposit on a group of chosen electrodes on a support, among amultiplicity of electrodes on the support. In accordance with thisprocess:

a support is used having on its surface the multiplicity of electrodesand comprising an electric shield, called earth shield, formingrespectively with the multiplicity of electrodes a multiplicity ofcapacitors,

a group of capacitors corresponding to the group of chosen electrodes ischarged by depositing electric charges on these electrodes,

the support is placed in the presence of an electrolyte to causeelectrolytic depositing on the electrodes corresponding to the chargedcapacitors, the electric charges deposited on the electrodes andrespectively stored in the corresponding capacitors supplying anelectrolysis current for each chosen electrode.

With the process of the invention, the substrate may do without anaddressing system for the electrodes. The charges may be depositeddirectly on the electrodes and stored in the capacitors formed by theseelectrodes and the earth shield. To deposit the electric charges, anelectric voltage, so-called polarization voltage is, for example,applied between the earth shield and the chosen electrodes.

Also, since the charges are deposited prior to bringing the support intothe presence of an electrolyte, the addressing or polarization of theelectrodes during electrolysis is avoided. This therefore eliminatesproblems connected with protecting and insulating the contactconnections for polarization and addressing in relation to theelectrolyte.

The supply of electrolysis current is not made by an outside generatorbut comes directly from the charges stored in the capacitorscorresponding to the chosen electrodes.

According to one aspect of the invention, during the electrolysis stage,the support may be immersed in an electrolytic bath or a mediumcontaining the electrolyte, and the earth shield may be placed incontact with an electrolysis counter-electrode also immersed in theelectrolytic bath.

According to one variant, the earth shield may be used directly as anelectrolysis counter-electrode. In this event, the electrolysis supportmay either be immersed in an electrolytic bath or simply moistened withthe electrolyte. For example, a thin film of electrolyte in contact withthe electrodes and with at least one part of the earth shield, may bespread over the surface of the support.

According to another particular aspect of the invention, in order toselectively charge a group of capacitors, a polarizing head is usedhaving a multiplicity of contact pads able to come into contactrespectively with the multiplicity of electrodes, the polarizing headbeing positioned on the support in such manner as to place eachelectrode of the electrolysis support in contact with a correspondingcontact pad of the polarizing head, and so as to bring the earth shieldinto contact with at least one earth contact pad in the polarizing head,and a polarizing voltage being selectively applied between each chosenelectrode and the earth shield via the contact pads.

The polarizing head may comprise an addressing system, for example ofmultiplex type, for the selective application to the contact pads ofpolarizing voltages that are suitable for charging the supportelectrodes.

When the electrodes, and therefore the capacitors, of a support havebeen charged using the polarizing head, the head is separated from thesupport and may be used again for other supports.

Therefore, the addressing system of the polarizing head is not asingle-use system.

A further purpose of the invention is an electrolysis support toimplement the above-described process. The electrolysis supportcomprises a multiplicity of electrodes and an electric shield, so-calledearth shield, that is electrically insulated from the multiplicity ofelectrodes and forms with said multiplicity of electrodes a multiplicityof capacitors. The electrodes and/or the earth shield, on which thecharges are deposited may be in the form of an electric conductormaterial deposited on an insulating support.

As an example, according to one particular embodiment, the electrolysissupport may comprise a support plate, a layer of electric conductormaterial deposited on the support plate forming the earth shield, alayer of electric insulating material placed on the layer of conductormaterial, and a multiplicity of electrodes of electric conductormaterial positioned on the layer of insulating material.

The electrodes, separated one from the other, are mutually insulated andare insulated from the earth shield by the layer of insulating material.

The earth shield forms a common electric plate in relation to which eachindividual electrode forms a capacitor, and the layer of insulatingmaterial forms the dielectric of the capacitors.

According to one particular aspect, the layer of insulating material maycomprise at least one through hole in the areas without electrodes toexpose the earth shield in these areas. This characteristic is ofparticular interest when the earth shield is used as a counter-electrodefor electrolysis. In this case, for example, one portion of thecounter-electrode may be placed in the vicinity of each electrodethereby assuring reliable, homogeneous depositing.

The openings may be designed as grooves individually surrounding eachelectrode.

According to one variant, the electrodes and/or the earth shield mayalso be in the form of doped zones formed by setting in a semiconductorsupport.

The electrolysis support may, for example, comprise a semiconductorsubstrate of a first type of conductivity and zones set in thesubstrate, having a second type of conductivity, opposing the first typeof conductivity.

The electric insulation between electrodes is, in this case, a junctiontype insulation. For example, if the substrate is of P conductivitytype, the electrodes are zones of N type. The substrate in this case isadvantageously connected to a fixed potential chosen to avoid electrodedischarge.

A further object of the present invention is a polarizing head which maybe used to implement the process.

The polarizing head comprises:

a front plate fitted with a multiplicity of contact pads placed so thatthey may be brought into contact respectively with the multiplicity ofelectrodes on the electrolysis support and with at least one earthcontact pad placed so that it may be brought into contact with a contactconnection of the earth shield,

addressing means for the selective application of a polarization voltageto a group of contact pads chosen from among a multiplicity of contactpads.

As indicated above, the addressing means may be of multiplex type. Theaddressing means may also comprise a network of connection lines toapply appropriate voltages directly to the contact pads using an outsidevoltage source.

According to one particular aspect of the invention, the polarizing headmay comprise a compression chamber. The front plate is then designed toform part of the wall of the compression chamber. The compressionchamber may be placed under pressure to cause slight deformation of thefront plate when the polarizing head is placed on the support, so thatthe contact pads may be firmly applied against the electrodes.

Other characteristics and advantages of the invention will be betterapparent from the following description with reference to the figures ofthe appended drawings that are given for illustrative purposes only andare not restrictive.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a section diagram of an electrolysis support for theimplementation of the process of the invention

FIG. 2 is a top view of the support in FIG. 1,

FIG. 3 is a section diagram of one variant of embodiment of theelectrolysis support for the implementation of the process of theinvention,

FIG. 4 is a section diagram of a polarizing head in accordance with theinvention for the implementation of the process of the invention,

FIG. 5 is a section diagram of the support in FIG. 1 and the polarizinghead in FIG. 4, and illustrates one stage of selective charging of theelectrolysis support in accordance with the process of the invention

FIG. 6 is a section diagram of an electrolysis bath containing anelectrolysis support in accordance with FIG. 1,

FIG. 7 is section view of a support in accordance with FIG. 3, andillustrates one stage of electrolysis on this support in accordance withthe invention.

DISCUSSION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an electrolysis support of the type used for the presentinvention. It comprises a multiplicity of electrodes 10 on which may beselectively deposited different compounds such as ligands. The lattermay either be oligonucleotide probes for the recognition of DNA targets,or antigenic probes for the recognition of antibody type targets, orchemical probes for the recognition of certain molecules such as heavyions, gases. The probes may either be grafted directly onto theelectrodes or grafted or trapped in a support network such as a polymer,for example of polypyrrole, polyaniline, polythiophene type, thesepolymers having conduction properties making grafting easier byelectrochemical means. With these deposits it is possible, for example,to fabricate biological or chemical sensors.

Electrodes 10 are formed on a layer 12 of insulating material whichinsulates them electrically from a layer of conductor material 14. Layer14 forms an earth shield whose function is specified below; it is termedearth shield 14.

Layer 12 of insulating material is for example a layer of silicon oxideSiO₂ approximately 50 to 100 nm thick.

Earth shield 14 and electrodes 10 may, for example, be fabricated in ametal chosen from among chromium, nickel, gold, aluminium or titanium.Other conductors may however be selected, in particular for the earthshield, in relation to the compounds or substances it is desired todeposit by electrolysis. The thickness of the electrodes and earthshield is chosen for example from between 50 to 100 nm.

The group of electrodes 10, of layer 12 and the earth shield issupported by a substrate plate 16.

Substrate plate 16, whose thickness is in the region of 0.1 to severalmillimetres, is made of a material such as silicon, glass or plastic forexample.

As shown in FIG. 1, earth shield 14 is not fully covered by layer 12 ofinsulating material, but one portion 18 of the earth shield, forming acontact connection is left exposed so that it is accessible through theside of the support comprising electrodes 10.

Each electrode 10 respectively forms a first capacitor plate and theearth shield forms a second plate, common to both capacitors. Thecapacitor associated with each electrode may therefore be charged byapplying an adequate polarization or charge voltage between earth shield14 and electrode 10 under consideration. The charges stored in thecapacitors provide the electrolysis current during electrolysis for eachelectrode respectively.

FIG. 2, a top view of the support, shows an array of electrodes in rowsand columns.

The electrodes in this layout are insulated from one another by thelayer of insulating material 12.

In the example of FIG. 2, each electrode 10 has a portion 10a calledactive zone, and an appendix 10b connected to the active zone. Activezone 10a is provided for the reception of an electrolytic deposit andpossibly to house a biological sensor or other sensing element dependingupon the end-purpose of the electrode support. The function of appendix10b on the other hand is essentially to serve as a contact connection.Appendix 10b is provided for the reception of a contact pad of apolarizing head described below, for the purpose of charging thecapacitor corresponding to the electrode.

Finally, FIG. 2 shows that, in the illustrated mode of embodiment,portion 18 of earth shield 14 forming a contact connection surrounds thelayer of insulating material 12 forming a border contour.

FIG. 3 shows a further possible embodiment of the electrolysis support.

In the mode of embodiment shown in FIG. 3, layer 12 of insulatingmaterial is etched so that openings 20 may be made on it betweenelectrodes 10. Openings 20, for example in the form of grooves, are usedto expose portions 22 of earth shield 14 in the vicinity of electrodes10. For example, each electrode may be surrounded by a groove cut in thelayer of insulating material.

The use of openings 20 and portions 22 of the earth shield that areexposed, becomes especially apparent during electrolysis when the earthshield is used directly as a counter-electrode for electrolysis. Thispoint is described in more detail below.

The capacitors associated with the chosen electrodes of the support maypossibly be charged one by one, in particular when there are fewelectrodes.

However, especially when there is a high number of electrodes, it ispossible to use a polarizing head for this operation, of which oneexample is given in FIG. 4.

The polarizing head comprises a front plate 30 fitted with amultiplicity of contact pads 32 in the form of beads and metal pads. Themetal beads are for example beads in indium-lead alloy. They are givenshape by heat treatment using a layer 31 of insulating material that hasno wetting properties vis-a-vis the beads and covers the surface offront plate 30.

The number of contact pads and the distribution of the contact pads 32on the surface of front plate 30 respectively correspond to the numberof electrodes 10 and the distribution of electrodes 10 on the surface ofan electrolysis support such as shown in FIGS. 1 to 3.

Therefore, when the polarizing head is positioned on the electrolysissupport, the beads which form contact pads come into contactrespectively with electrodes 10, and more precisely with appendices 10bof these electrodes.

The polarizing head also comprises one or several additional pads 34placed around the periphery, provided to come into contact with contactconnection 18 of earth shield 14 of the electrolysis support (see FIGS.1 to 3). Pads 34 are formed by beads having, in this example, a diameterthat is slightly larger than that of the beads forming pads 32.

Front plate 30, in silicon for example, may comprise an addressingelectronic circuit 40, connected to an outside voltage generator 42.Circuit 40, driven by an outside control computer 44, is designed toapply selectively to a chosen group of contact pads 32 a polarizingvoltage supplied by generator 42.

Addressing circuit 40 may comprise pad addressing rows and columns. Eachcontact pad is connected via a transistor to an addressing row andcolumn. Therefore, the application of the polarizing voltage to a givencontact pad results from activating the conduction of the correspondingtransistor. Such multiplex addressing is itself known as such and used,for example, to control liquid crystal display screens.

The addressing rows and columns are symbolically represented by achain-dotted line carrying the reference 46.

The rear surface of front plate 30 may be etched so that it has a slot48 in the area comprising contact pads 32.

Front plate 30 is also glued to a plate 52 which acts as cover for slot48. Plate 52 is also in silicon.

The slot thus forms a chamber, called a compression chamber 50, whosewalls are formed by the cover plate and front plate.

Compression chamber 50 is connected to a pressurized air inlet 54. Frontwall 30 is also designed with sufficient elasticity so that it undergoesslight deformation in response to pressurization of chamber 50. The useof this deformation can be seen in FIG. 5.

FIG. 5 shows the use of the polarizing head in FIG. 4 to selectivelycharge the capacitors corresponding to the electrodes of an electrolysissupport as in FIG. 1.

As is shown by FIG. 5, the polarizing head is positioned on the supportin such manner that each contact pad 32 comes up against a correspondingelectrode 10 of the electrolysis support, and so that additional pads 34come up against contact connection 18 of the earth shield. It will benoted in this respect that the slightly larger diameter of the beads ofcontact pads 34 allows for compensation of the thickness of the layer ofinsulating material 12 and the thickness of electrodes 10.

When the polarizing head is positioned and maintained mechanically (asis the case in microelectronics aligning machines) against theelectrolysis support, pressurized air enters compression chamber 50. Thepressure established in chamber 50 exceeds surrounding pressure by 0.1bar or more.

Under the effect of the pressure, the front plate undergoes slightdeformation in the direction of the support comprising the electrodes.Contact pads 32 are therefore firmly applied against electrodes 10. Thisarrangement guarantees good contact between these parts.

When contact between the contact pads and the electrodes is established,the addressing circuit is operated so that it applies an earth (orground) voltage to earth shield 14 of the electrolysis support andapplies a voltage V to the chosen electrodes. The earth voltage isapplied to the earth shield via contact pads 34 while voltage V isapplied to the chosen electrodes by contact pads 32. Advantageously, anearth voltage may also be applied to non-selected electrodes.

The capacitors associated with the electrodes receiving polarizationvoltage V store a charge Q such that Q=CV, in which C is the capacity ofthe capacitor associated with each electrode. The capacitors associatedwith the electrodes which receive a polarizing voltage, equal to theearth voltage (non-selected electrodes) store a zero charge.

The polarization of the chosen electrodes may be concomitant orsequential.

FIG. 6 shows a subsequent stage of the process of the invention which isthe electrolysis stage. The electrolysis support whose capacitorscorresponding to the chosen electrodes are charged, is immersed in atank 60 containing an electrolytic bath 62.

A counter-electrode 64 is also immersed in the bath and electricallyconnected to earth shield 14 of the electrolysis support.

Electrolysis takes place by transfer of stored charges in the capacitorsassociated with the selected electrodes. Charge transfer takes placebetween the chosen electrodes and the counter-electrode and causes theformation of an electrolytic deposit 66 on the chosen electrodes. In theFigure, charge transfer is symbolized by the arrows.

FIG. 7 shows a variant of implementation of the electrolysis stage usingan electrolysis support according to FIG. 3.

In the case shown in FIG. 7, only a thin film of electrolyte 70 isdeposited on the surface of the support comprising electrodes 10. Theelectrolyte film wets the group of electrodes 10 and the earth shield onportion 18 forming a contact connection and in openings 20.

In the case shown in FIG. 7, the earth shield forms thecounter-electrode for electrolysis.

Charge transfer, symbolized by arrows, takes place between the earthshield (in openings 20) and the chosen electrodes 10.

Charge transfer creates an electrolytic current which allows formationof a deposit 66 on the chosen electrodes. When the capacitorscorresponding to the chosen electrodes are discharged under the effectof the electrolysis current, depositing stops.

The electrolysis support is then rinsed and dried. It may undergo a newcharge with the polarizing head choosing other electrodes for a furtherdeposit of different material for example.

In this way the electrolysis support may selectively undergo severaldeposits with different electrolytes.

List of Documents Cited in This Application

(1) <<Fluxless Flip-Chip Technology>> by P. Caillat and G. Nicolas--LETI(CEA-Advanced technologies)

(2) <<Array of individually addressable microelectrodes>> by G. C.Fiaccabrino et al. In <<Sensors and Actuators>> B, 18-19, pp. 675-677

(3) WO 94/22889

I claim:
 1. A process for the electrolytic formation of a deposit on agroup of electrodes of a support chosen from among a multiplicity ofelectrodes on the support, wherein the support used has on its surfacethe multiplicity of electrodes and comprises an electrically conductiveplate respectively forming with the multiplicity of electrodes amultiplicity of capacitors, comprising:selectively charging a group ofcapacitors corresponding to the group of chosen electrodes by depositingelectric charges on the group of electrodes; and placing the support incontact with an electrolyte to cause electrolytic depositing on theelectrodes corresponding to the charged capacitors, the electric chargesdeposited on the electrodes and stored in the corresponding capacitorsrespectively providing an electrolysis current for each of the chosenelectrodes.
 2. A process in accordance with claim 1, comprising:using anelectrolysis counter-electrode in electrical contact with the plate. 3.A process in accordance with claim 1, comprising:using the plate as acounter-electrode for electrolysis.
 4. A process in accordance withclaim 1, comprising:in order to selectively charge said group ofcapacitors, using a polarizing head having a multiplicity of contactpads able to come into contact respectively with the multiplicity ofelectrodes, positioning the polarizing head on the electrolysis supportin such manner as to bring each electrode of the electrolysis supportinto contact with a corresponding contact pad of the polarizing head,and bringing the electrically conductive plate into contact with atleast one contact pad of the polarizing head, the charges beingdeposited selectively on the chosen electrodes via contact pads.
 5. Asystem, comprising:an electrolysis support having a multiplicity ofelectrodes and an electrically conductive plate, electrically insulatedfrom the multiplicity of electrodes, the electric plate forming withsaid multiplicity of electrodes a multiplicity of capacitors; a frontplate fitted with a multiplicity of contact pads, placed in such mannerthat they may be placed in contact respectively with the multiplicity ofelectrodes on the electrolysis support, and with at least one contactpad positioned so that it can be brought into contact with a contactconnection of the plate; and addressing means to selectively apply apolarizing voltage to a group of contact pads chosen from among themultiplicity of contact pads.
 6. A system in accordance with claim 5, inwhich, in the electrolysis support, the electrodes and/or the plate areformed of an electric conducting material.
 7. A system of claim 5,wherein said support comprises a support plate, said electricallyconductive plate comprising a layer of electric conducting materialplaced on the support plate forming an earth shield, a layer of electricinsulating material placed on the layer of conducting material, and themultiplicity of electrodes comprising an electric conductor materialplaced on the layer of insulating material.
 8. A system in accordancewith claim 7, in which the layer of insulating material comprises atleast one opening in the areas without the electrodes to expose theearth shield in these areas.
 9. A system in accordance with claim 8,wherein the opening is a groove surrounding each of the electrodes. 10.A system in accordance with claim 5, in which the electrodes and/or theplate are doped zones of a semiconductor support.
 11. A system inaccordance with claim 10, comprising a semiconductor substrate of afirst conductivity and zones set in the substrate having a secondconductivity, opposed to the first conductivity.
 12. A system inaccordance with claim 5, in which the contact pads comprise contactbeads.
 13. The system of claim 5, wherein the plate comprises an earthshield.
 14. A polarizing head, comprising:an electrolysis support havinga multiplicity of electrodes and an electrically conductive plate; afront plate fitted with a multiplicity of contact pads, placed in suchmanner that they may be placed in contact respectively with themultiplicity of electrodes on the electrolysis support, and with atleast one contact pad positioned so that it can be brought into contactwith a contact connection of the plate; addressing means to selectivelyapply a polarizing voltage to a group of contact pads chosen from amongthe multiplicity of contact pads; and a compression chamber, the frontplate forming one portion of a wall of the compression chamber, and inwhich the compression chamber may be placed under pressure to produceslight deformation of the front plate when the polarizing head is placedon the electrolysis support, so that the contact pads may be firmlyapplied against the electrodes.
 15. The system of claim 14, wherein theplate comprises an earth shield.